U.S. Pat. No. 4,940,972, describes displaying to a pilot of an aircraft a synthetic image of the ground terrain over which the pilot is flying. U.S. Pat. No. 5,566,073 describes allowing a pilot to preview a route either in flight or on the ground. The '073 patent also describes allowing the pilot to take over and try out different flight strategies. The data volume required to display flight routes in accordance with the above-mentioned patents is very large. The '073 patent describes representing the terrain as polygons in order to save computer storage space, but even so, the amount of storage on most home computers allows only a limited area and/or resolution level to be displayed. The '073 patent describes using a CD-ROM to store the required data, but the delivery of the CD-ROM to home users requires time and changes in the terrain (such as seasonal changes) can require frequent updates of the data on the CD-ROM.